Precision control of timing elements such as delay elements, oscillators and one shots is a typical design requirement in digital and analog integrated circuits. There are two common methods of providing for the precise control of such timing elements. The first method uses conventional digital synchronization of the elements with an external reference clock signal. The second technique uses precision components such as resistors and capacitors to set up a time constant. Both of these techniques have severe limitations for the integrated circuit environment.
A typical application of the digital technique of synchronization would be to gate an event such as an incoming pulse with another timing pulse whose period is set to an integer multiple of the reference clock. The drawbacks of this method are that the controlling pulse can only be an integer multiple of the reference clock. This problem can only be mitigated by using an extremely high frequency reference clock so that a "one clock cycle" error is insignificant relative to the event being gated.
Significant difficulties arise using the analog approach as well. Precise control of the values of resistors, inductors and capacitors have not been achieved in high volume semi-conductor techniques which are common to integrated circuit implementation. The precision of the synchronization of various elements within the integrated circuit is directly related to the precision of the value of the aforementioned components. Precise control of the values of these elements can only be achieved via laser trimming of on-chip components or through the use of external components. Both of these methods are extremely expensive when compared to normal semi-conductor processing costs.
Accordingly, a need has arisen for a system which can provide time reference signals to remote locations on an integrated circuit chip which does not require extremely high frequency reference clock signals, precision external timing components or precision adjustment of internal components via laser trimming or other methods.